Pseudomonas aeruginosa is known to be naturally resistant against most of antibiotics commonly used. Although there are only a few antibiotics to which the bacteria are sensitive, the use of these antibiotics in the therapy of infections due to Pseudomonas aeruginosa is not effective in most cases when the hosts are physiologically immature in immune response or in these cases in which the hosts are being treated by administration of medicines which deteriorate their immune mechanisms.
Mink infection due to Pseudomonas aeruginosa is well known as a so-called hemorrhagic pneumonitis. For the purpose of protecting mink from this contagious disease, minks were usually immunized with the formalin-killed bacteria which had been isolated from mink killed by the endemic disease. However, the effect of this vaccine has been doubtful. Therapy by means of antibiotics effective against the bacteria is usually not applicable, because its administration for only a few times is insufficient for preventing the natural development of the endemic disease, and repeated administrations at 2-3 day intervals are impossible. Generally speaking, there are thousands of minks in one farm and only special technicians can manage the vaccination of the mink. The high cost of the drugs is another reason for the unsuitability of antibiotics for this purpose.
As to bovine mastitis, there was a case in which antibiotics were administered continuously, but the cost involved was excessive. An acute case may be treated with antibiotics, but most chronic cases can hardly be treated in this way.
The radical treatment of mastitis infected by Pseudomonas aeruginosa could not be achieved by antibiotics alone because of the recurrence of infection after the temporary success of the treatment.
The formalin-killed vaccine used so far is also unsatisfactory in that this vaccine is merely capable of preventing or treating infection by the same homologous serotype strain as that from which the vaccine was derived. Since more than 13 kinds of serotype (O antigen) are known in Pseudomonas aeruginosa and a specific O antigen can protect animals only against infection by the homologous O serotype strain, this particular vaccine cannot be prepared in advance for prophylactic (therapeutical) purposes. Once there occurs the endemic disease due to Pseudomonas aeruginosa, approximately 30-50% minks in a farm die because of hemorrhagic pneumonitis.
On the other hand, it has been proved that an immune state of a host is a very important defense factor against infection due to Pseudomonas aeruginosa. As for immunotherapy using vaccine and plasma against Pseudomonas aeruginosa infection, there have been published many papers, reporting that both active and passive immunization are effective against Pseudomonas aeruginosa in certain types of infection caused by the bacillus. The lipopolysaccharide (LPS) derived from Pseudomonas aeruginosa is protective only against infection with the same serotype strain as that from which it is derived. Therefore, several several LPSs had to be admixed in order to develop a vaccine for use against all the types of Pseudomonas aeruginosa infection.
The present invention is based upon the finding that the component OEP consisting mainly of protein is capable of preventing infection by all the serotype strains belonging to Pseudomonas aeruginosa.